Effect of response surface parameter variation on structural reliability estimates

In the reliability estimation of complex structures, response surface methodology has been suggested as a way to estimate the actual but implicit limit state function. Typically the response surface is constructed from a polynomial function and fitted to the implicit function at a number of points. The location of these points has been noted as being an issue but the effect of varying their location has had little attention in the literature. In the present paper some simple examples are used to indicate possible effects. It is noted that the probability can be both under- and over-estimated, depending on the choice of points, but that no clear guidance for point selection can be given in any one case. A particularly disturbing feature is that for some types of problems there can be instability in the probability estimate as the location of the points is changed. This is demonstrated through a previously well-discussed example.